Copper (Cu) has been used as an interconnection material in order to reduce the resistance of interconnections. In the case of forming a copper interconnection, a damascene process is generally used. In the damascene process, chemical mechanical polishing (CMP) may be performed, and after the CMP process is performed, a thin copper oxide film may be formed on the copper interconnection. A copper oxide film may be formed because it is difficult to completely intercept oxygen during the CMP process, and slurries used in the CMP process typically contain oxygen components. If a copper oxide film exists on the copper interconnection, the adhesion of the copper connection to a layer deposited on the copper interconnection may be degraded, and the interconnection resistance may be increased, thereby deteriorating the reliability of the semiconductor device.
Generally, in order to remove the copper oxide film, a plasma process may be performed with respect to a semiconductor substrate. If the plasma process is performed with respect to the semiconductor substrate, carbon components of an insulating layer may be removed by the plasma, and thus the carbon content of the insulating layer may be reduced. Also, a low dielectric material (i.e., a low-k material) that is mainly used as a material of the insulating layer may be porous and have a low mechanical solidity. Accordingly, when a plasma process is performed with respect to the insulating layer formed of a low-k material, the porosity of the insulating layer may be further increased if carbon is removed therefrom, and this increase in porosity may decrease the reliability of the semiconductor device.
Typically, in order to completely remove a copper oxide film, a long-time plasma process is required. However, as the plasma process is performed for a longer time, the thickness of the insulating layer being damaged by carbon removal becomes greater. Accordingly, if the plasma process is performed for a long time to completely remove the copper oxide film, the thickness of the damaged insulating layer, for example, may be about 1000 Å.
If the thickness of the damaged insulating layer is increased, then electron movement therein may occur and cause current leakage to neighboring interconnections. The porosity of the insulating layer may also be increased and thereby shorten the lifetime of the device. However, if the plasma process is weakly performed in order to reduce the thickness of the damaged insulating layer, the copper oxide layer may not be completely removed. Consequently, there is a need for a technique that can make the damaged insulating layer thin while completely removing the copper oxide layer.